688
Energy & Fuels 1991,5,688-694
gasification reaction intensively takes place mainly on the sites in contact with CaO. When this sample is outgassed at 900 K to stop the gasification reaction, most of the Cf remains as it is. If the sample is cooled under 1802 gas as in Figure 5b, all the Cf would be converted to C ( W ) which will desorb as C'% around 980 K in the subsequent TPD. Therefore, the amount of Cl80 evolution differed very much between the two W D runs in Figure 5, but the peak temperature of the main Cl80 evolution was not so different. The 1602 gasification of a '%,-gasified sample can also be reasonably interpreted by the proposed scheme. In the gasification, active l60produced on initial stage of 1802 CaO attack C('80) which was formed in the previous '80, gasification and the sites in the interface between carbon and CaO are quickly converted to C(l60), and then the resultant C(l60) reacts with l60to produce C1602. These processes are so fast that we observed the rapid C1602 formation without the induction period as observed in Figure 2a. Active l60may happen to migrate to the area still covered with C('%), and produce C'W% via reaction 7. The resultant Cf is then converted to C(l60). Through this process, C(l80) is gradually replaced by C(lsO). The subsequent W D hence had Cl60 and C'% evolutions from C(l80) and C(l80), respectively, and the ratio of Cl60 to Cla0 increases with the gasification time as is seen in Figure 7.
Conclusions The addition of Ca enhanced the formation of CO, in carbon gasification with 0,.This CO, formation was explained from the following mechanism. First, O2 dissociatively chemisorbs on CaO particle to form CaO(0). The results of SIMS analysis support the presence of such dissociative chemisorption of 0,.The active oxygen from CaO(0) quickly migrates to the carbon surface to form C(0). When vacant sites, Cf, around CaO are replaced by C(O),most of active oxygen cannot migrate further, but they react only with the C(0) on the interface between carbon and CaO, followed by CO, evolution. CaO(0) + C(0) = CaO + C(0.0) C(O.0) = co, + Cf The important point of this mechanism is that carbon gasification intensively occurs only on the area in contact with the catalyst particle, and the gasification rate of other sites is very low. In other words, only a very small portion of C(0) participates in the COPevolution. Acknowledgment. The financial support of a Grantin-Aid for Scientific Research from the Ministry of Education, Science and Culture, Japan (No. 62550552 and 63603014), is acknowledged. Registry No. Ca, 7440-70-2;COz, 124389; graphite, 7782-42-5.
Chemical Structure and Petrology of Resinite from the Hiawatha "B"Coal Seam John C. Crelling,t Ronald J. Pugmire,$ Henk L. C. Meuzelaar,**§ William H. McClennen,§ Huaying Huai,! and Jirina Karas* Department of Geology, Southern Illinois University, Carbondale, Illinois 62901, Department of Fuels Engineering, University of Utah, Salt Lake City, Utah 84112, and Center for Micro Analysis and Reaction Chemistry, University of Utah, Salt Lake City, Utah 84112 Received February 16, 1988. Revised Manuscript Received May 30, 1991
The objective of the present study is to examine the chemical structure and composition of Utah Wasatch Plateau coal resinite. Macerals were separated from the coal matrix by hand picking, sink-float treatments, and/or density gradient centrifugation (DGC). DGC separation was found to produce highly purified resinite fractions. Resinite-rich Wattis Seam coal samples were collected from fresh mine faces and, after varying degrees of concentration, subjected to '3c magic angle spinning NMR, Curiepoint pyrolysis MS, and Curiepoint pyrolysis GC/MS in addition to petrographic analysis and fluorescence microscopy as well as conventional (e.g., ultimate analysis) characterization methods. The data obtained confirm recent findings indicating that the abundant blue/green fluorescing resinite component is a polymeric substance composed of sesquiterpenoid repeat units with a median size of 204 Da, corresponding to the empirical formula ClbHZ4.The monomeric sesquiterpenoid units obtained during pyrolysis appear to represent different degrees of unsaturatization ranging from C16HB sesquiterpenes to the aromatic C16H18cadalene. Clearly, sesquiterpenoids constitute the bulk of extractable resinite in Wasatch Plateau field coal and are likely to be important precursors of the abundant extractable alkylnaphthalene moieties in such coal.
I. Introduction Although the maceral resinite occurs in most U.S. coals, it is particularly abundant in the coal seams of the Wasatch Plateau coal field in central Utah. The high resinite 'Southern Illinois University. Department of Fuels Engineering, University of Utah. Center for Micro Analysis and Reaction Chemistry, University of Utah.
*
content of the coals of central Utah has long been known and commercially exploited but little work has been reported on the elucidation of the chemical composition of this material. The resinite occurrences have been described by Spieker and Baker,' Tomlinson,?Thiessen and Sprunk? and Buranek and Crawford.' An unusual feature (1) Spieker, E. M., Baker, A. A. US.Geol. Swv. Bull. IS%, 796-C,125. (2) Tomlinson, H.U.S. Bur. Mines Rep. of Inv. 3189; 1932, pp 91.
0887-0624/91/ 2505-0688$02.50/0 0 1991 American Chemical Society
Structure and Petrology of Resinite
of the coal seams in Utah is that most of the resinite occurs in a secondary manner as cleat, fissure, or other void fillings. Similar occurrenceshave been reported in British coals by Jones and Murchison6and Murchison and Jones! They concluded that the metamorphic effects of coalification in the bituminous rank range caused the resinite to be gently mobilized without the more severe manifestations of metamorphism such as vesiculation or increased reflectance. Teichmuller7s8observed that secondary resinite (exudatinite) seemed to be exuded from other coal macerals during coalification in the lower bituminous range. In a recent review of the geochemistry of resinites, Givens reported that resinite is derived from terpenoid plant resins that have polymerized in situ and that it has a predominantly aliphatic character. MurchisonlOwas able to distinguish between resinites of bituminous coals and those of lower rank coals on the basis of infrared spectral analysis. These IR data suggest that resinites from a number of lignites are quite similar to the fossil resins (e.g., ambers) as well as to the subfossil or recent resins (e.g., copals). He found that the lower rank resinites lack a strong vibration at 1600 cm-' (due to aromatic skeletal vibration) that is present in bituminous coals. The resinites of both groups of coals showed a strongly aliphatic nature, however. The higher plants contain terpenoid substances commonly known as resins. These terpenoid resins from both gymnosperms and angiosperms may polymerize an exposure to air and the polymerization in situ in dead plants gives rise to the resinite maceral found in almost all coals but more particularly in the coals of the Cretaceous and Tertiary ages. These resins are very durable and massive occurrences of fossilized materials not associated with coal deposits are popularly known as amber."J2 Beck has reviewed the amber literature and presents extensive IR data on ambers from 12 European countries. These data are interpreted as establishing the basic structure of Baltic amber as a labdatriene polymer.12 A detailed discussion of the botanical affinities of various ambers and coal associated resins can be found in the work of Langenheim.13 Details of the chemical structure of the micropetrographically defined maceral resinite have generally been lacking because it is noncrystalline and is only partially soluble in organic solvents. Hatcher et al.14 have used cross-polarization magic angle (CP/MAS) 13CNMR as an analytical tool to compare the general structural features of coal resinite with fossil amber. Lambert and Frye16J6 have used CP/MAS NMR data to describe the functionality in amber and noted significant structural variations based on the source of the sample. Cunningham et al." (3)Thieawn, R.; Sprunk, G. C. U.S. Bur. Mines. Tech. Pap. 573;1937, 34 PP. (4)Buranek, A. M.; Crawford, A. L. Utah Geol. Mineral. Suru. Mono. Ser. 1962,No. 2, 3. (5)Jones, J. M.; Murchison, D. G. Econ. Geol. 1963,58,263. (6)Murchison, D. G.;Jones, J. M. Adu. Org. Geochem. 1962,1964,l. (7)Te/chmdler, M.Fortschr. Geol. Rheinl. Westfalen 1974,23,37. (8) Teichmdler, M. Adu. Org. Geochem. 1973,379. (9) Given, P. H. An Essay on the Organic Geochemistry of Cool, i? Coal Science; Gorbaty, M. L., Larsen, J. W., Winder, I., Eds., Academic Presa: New York. 1984: Vol. 3. (10)Murchison, D.. J: Adu.Chem. Ser. 1966,55,307. (11)Cunningham, A.; Gay, I. B.; Oehlschlager, A. C.; Langenheim, J. A. Phytochemistry 1983,22,965. (12)Beck, C. W. Appl. Spectrosc. Reu. 1986,22,57. (13)Langenheim, J. Am. Sei. 1990,78, 16. (14)Hatcher, P. G.;Breger, I. A.; Dennis, L. W.; Maciel, G.E. Prepr. Pap.-Am. Chem. SOC.,Diu. Fuel Chem. 1982,27,172-183. (15)Lambert,J. B.; Frye, J. S. Science 1983,217,55. (16)Lambert,J. B.; Frye, J. S.; Poinar, Jr., G. 0. Archaeometry 1986, 27,43.
Energy & Fuels, Vol. 5, No.5, 1991 689
have also employed NMR experiments to study variations in the chemical structural in amber from the Dominican Republic and Mexico and conclude that the resinous substance originates from a polylabdane Structure. Wilson et al.17 have presented an in-depth study of resinite from Yallourn brown coal (Australian). They conclude that the resin is a polymerized diterpenoid structure formed by the polymerization of agathic acid. More recently, their conclusion has been challenged by Anderson et al.18 who propose a polycommunic acid structure instead. The most comprehensive chemical studies of fossil resins by means of modern spectroscopic and chromatographic techniques appear to have been carried out by Simoneit et al.lS2l who investigated a broad series of ambers, brown coals, and fossil woods of different ages and identified a wide range of terpenoids with affmities to several different botanical species. Tricyclic diterpenoids of the abietane and pimarane skeletal varieties were found to be the most prominant building blocks. Moreover, increased maturation of fossil resins appeared to be characterized by progressive polymerization rather than aromatization. However, as shown by Grantham et al.,22Brackman et al.,a and Mukhopadhyay and Gormly,%sesquiterpenoids and triterpenoids, rather than diterpenoids, can be important constituents of some resins associated with coal beds. In a Curie-point pyrolysis mass spectrometry study of 22 U.S.lignites representing the Gulf Province and the Northern Great Plains province, Metcalf et al.= reported the presence of the biomarker retene (thought to be derived from abietic acid or related diterpenoid resinous matter) in Northern Great Plains lignites only. Nip et al.= described abundant amounts of low molecular weight sesquiterpenoids and diterpenoids as well as the biomarkers cadalene (MW 198)and retene (MW 234)in an Anderson seam lignite (PSOC 975)analyzed by gas chromatography/ mass spectrometry (GC/ MS). In contrast with the abundance of spectroscopic and chromatographic data available on some of the better known f w i l resin types,e.g., Baltic amber, Utah coal resins appear to have generated relatively little interest among coal scientists. Besides a 1984 publication by Mukhopadhyay and GormlyU and a density gradient centrifugation study by Bodily and Knopp,n few analytical data are available on Utah (Wasatch Plateau coal field) resinite. Practically without exception, the above-discussed literature reports have demonstrated that coal resinites and amber are composed of highly aliphatic and/or alicyclic
Geochem. 1986,7,161. (18)Anderson, K. B.; Botto, R. E.; Dyrkacz, G.R.; Hayatsu, R.; Winana, R. E. Prepr. Pap.-Am. Chem. SOC.,Diu. Fuel Chem, 1989,34(3), 752-758. ._ (19)Simoneit, B. R.; Grimalt, J. 0.;Wang, T. G., Cox, R. E.; Hatcher, P. G.;Nieeenbaum, A. Org. Geochem. 1986,10,877-889. (20)Grimalt, J. 0.; Simoneit, B. R. T.; Hatcher, P. G.; Nissenbaum, A. Org. Geochem. 1988,13,Nos. 4-6,677-690. (21)Grimalt, J. 0.; Simoneit, B. R. T.;Hatcher, P. G. Phytochemistry 1989,28(4),1167-1171. (22)Grantham, P. J.; Dough, A. G. Geochim. Cosmochim.Acta 1980, 44,1801-1810. (23) Brackman, W.; Spaargaren, K.; van Dongen, J. P. C. M.; Couperus, P. A.; Baker, F. Geochim. Cosmochim. Acta 1984,48,2483. (24)Mukhopadhyay, P. K.;Gormly, J. R. Hydrocarbon Potential of Two Types of Resinite. Adu. Org.Geochem. 1984,6,439-454. (25)Mctcalf, G. S.;Windig, W.; Hill, G. R.; Meuzelsar, H. L. C. Int. J . Coal Geol. 1987,7, 245-268. (26)Nip, M, DeLeeuw, J. W.; Schenk, P. A,; Meuzelaar, H. L. C.; Stout, S. A.; Given, P. H.; Boon, J. A. Curie-point Pyrolysis Maee Spectrometry, Cwie-point Pyrolysis-GM Chromatography-MeeeSpectrometry and Fluoreacence Microecopy ae Analytical Toole for the Charactarization of Two Uncommon Lignites. Anal. Appl. Pyrol. 1986,8,221-239. (27)Bodily, D. M.; Kopp, V. Prepr. Pap.-Am. Chem. SOC.,Diu. Fuel Chem. 1987,32(1),554-557.
Crelling et al.
690 Energy & Fuels, Vol. 5, No. 5, 1991 Table I. Elemental Analysis of Wattis Resinite C H N Ob 5% compositiono 85.63 10.39 0.71 3.27 standard deviation 0.08 0.07 0.23 Average of four determinations. Determined by difference.
materials. LamberP has provided quantitative information on the relative amounts of the following types of carbons found in amber: saturatedunsaturated:carbonyl. This triple ratio on various ambers is reported to be in the ranges of 83.5:11:5.5to 90.581.5where the carbonyl ratio varies from 0 to 2% depending upon the particular amber. While the work of Wilson16 does not include such quantitative ratios, the spectra obtained exhibit relatively high quantities (ca.510%) of carbonyl groups. Lambert et al.16 have suggested that it might be possible to correlate the age of Dominican amber with the content of the exocyclic methylene groups observed (ca. 105 ppm) by '9c CP/MAS experiments. The overall objective of the present study was to examine the structure of Utah Wasatch Plateau coal resinite macerals that have been separated from the coal matrix, purified, and, most important, carefully characterized by fluorescence spectral analysis. The samples were then analyzed by means of CP/MAS 13CNMR and by Curiepoint pyrolysis in direct combination with mass spectrometry (Py-MS) or via preseparation by gas chromatography (Py-GC/MS). A more detailed report on the results of the Py-GC/MS studies, including a comparison with some other recent and fossil resin samples, is being published elsewhere.28 11. Experimental Section The samples used in this study were collected underground from active mines near the towns of Hiawatha and Wattis in central Utah. In this area the main coal seam, the Hiawatha, splits into three units. The lower unit, the Hiawatha seam, is overlain by the Hiawatha "A" or third seam, which in turn is overlain by the Hiawatha "B" or Wattis seam. All three units are mineable and have been exploited in this area. All three units also contain abundant resinite that is visible macroscopically. At one exposed long-wall mining face in the Wattis seam, approximately 200 g of the fracture filling resinite was hand picked. A. Sample Preparation a n d Petrographic Analysis. All of the samples were collected from a fresh mine face and quickly placed in water to prevent oxidation during transport and storage. To obtain a resinite sample of the highest purity, the hand-picked resinite from the Wattis seam was further processed. It was possible to eliminate most of the nonliptinite material using a sink-float proms. Employing the density gradient centrifugation (DGC) technique already described by Dyrkacz et and Karas et al.?l it was possible to obtain fractions from the float portion of the sample that appeared to be composed only of resinite upon examination by fluorescence microscopy. The elemental analysis of the resinite float is given in Table I. The density distributions of the raw coal, the hand-picked sample, and the final resinite concentrate shown in Figure 1, a, b, and c, respectively, graphically demonstrate the efficiency of the DGC technique in separating this maceral. B. Petrography and Fluorescence Analysis. The maceral composition and rank of the whole coal sample were determined by standard maceral point counting and reflectance methods. The liptinite maceral composition was also determined with fluores(28)Meuzelaar, H. L. C.; Huai, H.; Lo, R.; Dworzmki, J. Chemical
Composition and Origin of Fossil Resins from Utah Wasatch Plateau Coal. Submitted to Fuels Process. Technol. (29)Dyrkacz, G. R.; Horwitz, E. P. Fuel 1982,61, 3. (30)Dyrkacz, G. R.; Bloomquist, C. A. A.; Ruscio, L. Fuel 1984,63, 1367. (31)Karaa, J.; Pugmire, R. J.; Woolfenden, W. R.; Grant, D. M.; Blair, S.Int. J. Coal Geol.1986,5,315. ~~
8
7 r\
HAND.PICKED RESINITE
o L 1000
1.050
1.100
1,150
1,200
1,250
1.300
DENSITY, pm/ml
Figure 1. Density distribution of resinite samples: (a, top) whole seam coal sample; the large peak on the right represents the dominant vitrinite macerals and the smaller peak on the left is from the resinite macer& (b, middle) hand-picked resinite; the vitrinite peak on the right represents vitrinite that could not be avoided in the collection process; (c, bottom) the pure resinite fraction obtained by the density gradient centrifugation of the float fraction of the hand-picked resinite sample. Table 11. Results of Petrographic Analysis of Whole Coal white blue maceral light, % light, % combined, 5% vitrinite 72.5 64.2 pseudovitrinite 11.6 10.3 9.6 semifuainite 10.8 semimacrinite 0.9 1.0 0.4 0.5 fusinite macrinite 0.0 0.0 micrinite 0.0 0.0 exinite 3.1 resinite 0.5 sporinite 3.1 3.1 11.4 11.4 resinite (total) 8.3 green 8.3 1.2 yellow 1.2 orange 1.5 1.5 0.4 0.4 brown cutinite 0.1 0.1 28.1 fluorescing vitrinite 57.3 other total 100.0 100.0 100.0 ~~~
cence microscopy and the fluorescence spectra of the various resinite macerals were also determined by using methods previously described by Crelling.32 The results are given in Table I1 and are discussed below. C. NMR Analysis. The CP/MAS studies were carried out in a Bruker CXP-100 aa described previously.= Data from a variable contact time experiment were obtained in the manner described by Solum et alSs Suitable spectra are obtained by accumulating loo00 scans with a contact time of 1 ma and a 1-s recycle time. High-resolution 13C and 'H NMR spectra were obtained on saturated solutions of resinite in CDC13. The highresolution spectra were taken on a Varian SC-300 spectrometer. The saturated solution contained colloidal particles of the resinite (32)Crelling, J. C. Microscopy 1985,132, 251. (33)Wilson, M. A.; Pugmire, R. J.; Karas,J.; Alemany, L. B.;Woolfenden, W. R.; Grant, D. M.; Given, P. H. Anal. Chem. 1984,56,933. (34)Solum, M.S.;Pugmire, R. J.; Grant, D.M. Energy Fuels 1989, 3, 187.
Energy & Fuels, Vol. 5, No.5, 1991 691
Structure and Petrology of Resinite polymer which produced line broadening of both the 'H and '% spectra. No attempts were made to remove the colloidal material and only the 'H spectrum contained useful information. D. Mass Spectrometric Analysis. Mase spectrometric (MS) analyses of the resin concentrates were carried out by means of Curie-point pyrolysis (maximum temperature 610 "C, heating rate 100 K/s, total heating time 10 8 ) in combination with low-voltage (12 eV set value) electron ionization MS, using an Extranuclear 50000-1 quadrupole MS system, as described previously.26Fine suspensions of resin concentrates in methanol were prepared by hand grinding 2-mg sample aliquota in 1 mL of Spectrograde solvent. Five-microliterdrops of these suspensionswere applied to the ferromagnetic wire, air-dried under continuous rotation, and suhquently used in Curie-pointpyrolysis. The DGC purified resin sample was further analyzed by Curie-point pyrolysis in conjunction with gas chromatography/mass spectrometry (PyGC/MS). Py-GC/MS analysis was performed with a specially designed Curie-point pyrolysis reactor in combination with a 1 5 m fused silica, wide bore (0.32 mm i.d.) capillary column with 0.25 pm 5% phenyl methyl silicone bonded stationary phase (DB-5, J&W Scientific)and connected to an Ion Trap Detector (Finnigan MAT, Inc.) mass spectrometer. Py-GC/MS conditions were as follows: sample size 15 pg, Curie-point temperature 610 "C, temperature rise time 18, reactor housing temperature 120 OC, GC column flow 3 mL/min (He),temperature program 15 "C/min (from 30 to 300 "C),GC/MS interface and MS source temperature 225 "C, electron ionization mode, scanning rate 2 spectra/s (from m / z 50 to 240). A second set of Py-GC/MS conditions was used in order to observe large, intact oligomer structures, namely, column length reduced to 3 m (i.d. 0.22 mm temperature program 40 "C/min to 320 "C), reactor housing temperature 290 "C, interface and source temperature 250 "C, isobutane chemical ionization mode, scanning rate 2 spectre/s (from m/z 100 to 6501, other parameters unchanged. In this mode, all spectra scanned during a single run are summed in order to obtain an overall MW profile. Finally, in order to estimate the pyrolysis yield of resin concentrate samples as well as to check for the presence of eventual low MW components, a sample of sink-float concentrated, hand-picked Wattis resin was analyzed by thennogravimetry (TG) using a Mettler I Thennoanalyzer system. TG analpis conditions were sample weight 9.75 mg, He flow 50 mL/min, heating rate 10 OC/min. h i d u a l weight percent was determined by weighing the platinum crucible and residue after the TG run.
111. Results and Discussion A. Petrographic Analysis. Both the whole seam and the hand-picked resinite from the Hiawatha "B" (Wattis) seam were characterized petrographically. The results of the reflectance analysis on the whole coal sample yielded a value of 0.58% in oil which places the sample at a rank near the subbituminous/high volatile C bituminous boundary. The results of the maceral analysis in both white light and fluorescent light and in a combined analysis of the whole seam sample are given in Table 11. The results show that, unlike most North American coals, the dominant liptinite maceral is resinite rather than sporinite. In general, the resinite occurs in both primary forms as cell fillings in vitrinite and ovoid masses and in secondary forms as cleat and fissure fillings, and as void fillings in inertinite macerals. Fluorescence analysis of coals from the Hiawatha seam and other seams from Utah, Wyoming, and New Mexico reveals four distinct types of resinite occurring in both primary and secondary forms. These four resinite types have been classified in blue light by Crelling et al.,= Crelling,82and Teerman et al.% as type 1 (green-fluorescing, spectral peak = 460 mm), type 2 (yellow-fluorescing,spectral peak = 540 mm), type 3 (orange-fluorescing, spectral peak = 580 mm), and type 4 (35) Crelling, J. C.; Dutcher, R. R.; Lange, R.V. Utah Geol. Mineral. Suru. Bull. 1982, Zl8, 187. (36)Teerman, S.C.; Crelling, J. C.; Glaee, G.B. Int. J. Geol., in press.
Table 111. Results of Fluorescence Spectra Analysis of Resinite parameter mean value std dev peak, nm 460.00 0.70 red f green, Q 0.11 0.02 area left, % area right, % area blue, %
12.17 87.83 50.10 33.89 10.99 5.02
area green, % area yellow, %
area red, %
zw
0.88 0.88 2.07 2.62 0.93 0.70
Type 460
60
2oLL 0 450
500
550
600
650
700
WAVELENGTH (nm)
Figure 2. Fluorescence spectrum of the pure resinite fraction (type 1,spectral peak at 460 nm) used in this study. All of the resinite particles observed in this fraction displayed this same spectrum. (red-brown-fluorescing, spectral peak = 690 mm). Fluorescence spectral analysis shows that each type has a distinctive set of spectral properties which allow the resinite to be quantitatively discriminated. Similar analysis of the hand-picked resinite from the Hiawatha "B" (Wattis) seam shows that it is predominantly the type 1 (green-fluorescing)secondary resinite, with minor amounts of type 2 (yellow-fluorescing) resinite. Detailed petrographic examination of the hand-picked resinite reveals that it occurs as angular particles that contain numerous inclusions. These inclusions can be broken into three types. One type represents small fragments of coal macerals such aa fusinite. Another type consists of fibrous fragments that may show cell texture and appear to be plant fragments (the few pollen grains encountered fall into this category). The final type of inclusion is dark, dusty material that can sometimes show flow and zoning structures. When the hand-picked resinite is purified in the DGC process, the resulting product is exclusively the type 1 (green-fluorescing) resinite which has the fluorescence spectral properties given in Table III. The fluorescencespectrum of the purified resinite is shown in Figure 2. Unless otherwise noted, all of the analyses discussed in this paper were run on this purified resinite concentrate and the results, therefore, represent the properties of a petrographically verifiable single coal maceral-resinite type 1with a fluorescence spectral maximum at 460 nm. B. Pyrolysis Mass Spectrometry. Figure 3 shows the Curie-point pyrolysis mass spectra from the three stages in the preparation of the purified Wattis seam resinite. The spectrum of the hand-picked "raw" resinite in Figure 3b still resembles that of the Wattis coal (Figure 3a), although the typical sesquiterpenoid pattern at m / z 198/ 202/204/206has become much more prominent. Under the low-voltage electron ionization conditions used in these experiments, aromatic hydrocarbons give a considerably stronger response than hydroaromatic or alicyclic compounds.26 From previous quantitative studies of mixtures
Crelling et al.
692 Energy & Fuels, Vol. 5, No. 5, 1991 0)WATTIS SEAM COAL
4 204
1
202
it01 11 n r c
td HANDPICKED RESlNlTE
;?,
2 5
P W
tr 2 0
'012% 432
Id9
c) DGC PURIFIED RESlNlTE
191
m/z 190
,
,
,,I,,
,,7m,, , , , I,,
,
mh
m/z 200
Figure 3. Curie-point pyrolysis mass spectra of resinite concentrates and raw Wattis seam coal. Notice residual 'coal pattem" in hand-picked resinite (b).
of alkyl-substituted naphthalenes and decalins,37it can be estimated that the resin content of the hand-picked sample may be in the 50% range. By contrast, the spectrum of the DGC purified sample in Figure 3c, however, does not show major ion series which cannot be readily explained as resin-derived. In fact, molecular ion signals at m/z 206, 204, and 202 would seem to represent intermediate degrees of unsaturation between the fully saturated dicyclic sesquiterpane at m/z 208 (only present in minor quantities) and the aromatic C6 alkylnaphthalene at m / z 198, also known as the biomarker cadalene.% The proposed sesquiterpenoid nature of the Curie-point pyrolysis products is further supported by the Py-GC/MS data shown in Figure 4. In view of the many possible skeletal types (according to Simoneit,Ig no less than 30 structural typea with almost 70 leas common skeletons have been recognized), it is not feasible to positively identify individual sesquiterpenoids in the Py-GC/MS data without proper standard compounds and/or reference spectra. Nevertheless, it is relatively easy to identify the Py-GC/ MS peaks in Figure 4 as sesquiterpenoids, in view of their characteristic retention time window and mass fragmentation patterns. The mass spectra of the sesquiterpenoid peaks in the reconstructed (total ion current) chromatogram reveal that nearly all of these compounds have a characteristic isopropyl substituent which supports the proposed origin from a common precursor. By choosing selected ion chromatograms covering the typical molecular ion range between fully saturated sesquiterpanes ( m / z 208) and the fully aromatic cadalene biomarker ( m / z 198) within the characteristic retention time window for sesquiterpenoids, as demonstrated by Simoneit et al.,lga convenient overview is obtained of the entire suite of sesquiterpenoids produced by Curie-point pyrolysis (see Figure 4). The fact, however, that many of the sesquiterpenoid compounds seen in Figure 4 were also observed by Nip et al.% in the low-temperature distillate fraction of a Wyoming (Anderson Seam) lignite prompted us to obtain the thermogravimetry (TG) profile shown in Figure 5. This TG profile shows that we are dealing primarily with a stable, presumably polymeric, substance (37) Windig, W.; McClennen, W. H.; Hill, G. R.; Meuzelaar, H. L. C. Chemom. Intell. Lob. Syet. 1987, I , 151-165. (38) Gallegoe, E. J. Anal. Chem. 1971,43, 1151.
E
1
A
m/z202
m/z 204
Q
IOQ-
80
tB
-
60-
a
**
40-
20-
04
Figure 6. Thermogravimetry profiles of sink-float concentrated
resinite. Note nearly complete volatilization between 350 and
475 OC. For experimental conditions see text.
which undergoes thermal fragmentation at temperatures in excess of 400 "C. Moreover, nearly complete volatilization is observed with only minor (3%) char formation. In view of the fact that a hand-picked resin float sample had to be used for this analysis (due to the very limited quantities of the DGC purified sample available) most or all of the char residue in Figure 5 may well represent remaining impurities. Gas permeation chromatography analyses of an Indonesian coal resin reported by Brackman et alea also revealed the presence of a high MW component thought to represent a copolymer of sesquiterpenoid and triterpenoid monomers. Although triterpenoid constituenta are readily in Utah Wasatch Plateau resinite as well,28
Energy & Fuels, Vol. 5, No. 5, 1991 693
Structure and Petrology of Resinite
WAmS SEAM GREEN RESINKE
I@
388
ri
5b
mlz
Figure 6. loobutane chemical ionization MS profie of Curiepoint desorption and pyrolysis produds (T- 610 "C)of DGS resinite obtained by summing the mass spectra of the compounds eluting from a short capillary GC column. Note the prominent series of sesquiterpenoid monomers, dimers and trimers.
these constituents appear to represent less than 5-10% of the bulk material and are removed by flash distillation, indicating that they are not part of the polymer backbone structure. The TG curve in Figure 5 is typical of a thermoplastic polymeric material, thus suggesting that the low molecular weight sesquiterpenoid fraction found in low-rank Western coals may polymerize during subsequent coalification stages. On the other hand, a polymeric fraction can also be observed in recent Dipterocarp resins (dammar gum) as described by Meuzelaar et al.,28suggesting that polymerization may already have occurred at the time of deposition. A further point of interest is that sesquiterpenoid moieties may well be the precursors of some of the extractable alkylnaphthalenes comprising up to 4% of fresh high-volatile bituminous Western coals.sg Similarly, the abundant aromatic and hydroaromatic picene-like constituents in Wasatch Plateau coal may be thought to have been derived from triterpenoid resin moieties, as discussed by Meuzelaar et aLZ8 However, it is highly unlikely that resinous components are entirely responsible for the extractable alkylnaphthalenes since similar extractable fractions are also encountered in high volatile to medium volatile bituminous coals from the Carboniferous period known to contain only minor amounts of resinous components upon micropetrographic analysis (Giveng). Finally, it should be pointed out that the various alkylnaphthalenes or hydroaromatic sesquiterpenoids (e.g., at m / z 202) are unlikely to have been converted to aromatic species during the pyrolysis procedure. Model compound studies'O4' indicate that aromatic ring formation through pyrolytic dehydrogenation is generally negligible under typical Curie-point pyrolysis/desorption conditions, even when alicyclic ring structures are present. Thus, the aromatic and hydroaromatic sesquiterpenoids at m/z 198 (cadalene) and m/z 202, respectively, are thought to represent existing structural moieties, whereas the sesquiterpenes at m/z 204 are the logical monomers of the proposed sesquiterpenoid polymer. Altogether, Figure 4 suggests that CISH1l ( m / z 204) sesquiterpenoids are most abundant followed by roughly equal concentrations of C15HB (m/z 206) and C15HB (m/z 202) sesquiterpenoids and a modest amount of CI5Hls(m/z (39) Meuzelaar, H. L. C.; McClennen, W. H.; Cady, C. C.; Metcalf, G.
5.;Windig, W.; Thurgood, J. R.; Hill, C. R. Pyrolysis Mechanisms and
Weathering Phenomena in Rocky Mountain Coals R e p r . Pap.-Am. Chem. SOC.,Diu. Fuel Chem. 1984,29, No. 5,166-177. (40) Meuzelaar, H. L. C.; Haverkamp. J.; Hileman, F. D. Pyrolysis Maas Spectrometry of Recent and Fossil Biomaterials, Compendium and Atlas; Elsevier Scientific: New York, 1982. (41) Richards, J.; McClennen, W. H.; Meuzelaar, H. L. C. J . Appl. Polym. Sci. 1987, 34, 1967-1975.
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I
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Figure 7. 13C CP/MAS spectrum of the pure green fluorescing Hiawatha resinite sample. The lower trace was obtained with a 40-ps interrupt in the proton decoupling. COMMERCIAL RESlNlTE
y
XI
8.0 71) 6.0 5.0 4.0 3.0 2.0 1.0 b PFWTMS Figure 8. 'H NMR spectrum taken at 300 MHz on a commercial resinite sample obtained from the Wattis seam. The sharp peak at 7.2 ppm is due to the deuterated solvent (99.8% CDC13).
198; cadalene). This is in close agreement with pyrolysis field ionization MS data4zas well as with the short column Curie-point pyrolysis chemical ionization MS data shown in Figure 5, which indicate a median ymonomer" (better perhaps: "repeat unit") size of 204 Da with a distribution skewed somewhat toward lower mass numbers sizes due to the presence of cadalene. In other words, the calculated average composition should lie somewhere around C16HD This is in excellent agreement with the overall H/C ration of 1.45 found by elemental analysis (see Table I). Especially noteworthy in Figure 6 is the absence of prominent peak series in the diterpenoid molecular weight range, e.g., m/z 250-320. This puts the (po1y)sesquiterpenoid Utah resinite in a rather different category than the predominantly (po1y)diterpenoidresins described by Simoneit and In fact, comparison of our findings with the data on Miocene Indonesian coal resins reported by Brackman et d.,29 Senftle et and Mukhopadhyay et al.= suggests a close chemical relationship between these resins, thought to be derived from angiosperm Dipterocarps, and the Upper Cretaceous Utah coal resins. The only other report of Dipterocarp coal resins in the U.S. appears to have been published by Saunders et al." who collected amber samples from Eocene lignite deposits within the Gulf Province. C. NMR Data. The CDP/MAS spectrum of the pure Wattis seam resinite is given in Figure 7. An fa value of 0.22 f 0.02 was obtained. The values for TCH(time constant for cross polarization) and TbH(the proton relaxation time in the rotating frame) for the aliphatic carbons, obtained from the variable contact time experiment were 0.10 f 0.01 and 27 f 2 ms, respectively, which are comparable (42) Anderson, L. L., personal communication. (43) Senftle, J. T.; Larter, S. R. Org. Chem. 1988, 13, No. 4-6, 973. (44) Saunders, W. B.; Mapes, R. H.; Carpenter, F. M.; Elaik, W. C. Geol. SOC.Am. Bull. 1974, 85, 979.
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694 Energy & Fuels, Vol. 5, No. 5, 1991
to the values reported by Botto et al.46for an Illinois No. 6 resinite maceral. From the break points in the spectrum, a number of peaks can be identified in the 0-50 ppm region. The peak at 18 ppm is due to methyl carbons on aromatic species while the peak at 24 ppm could arise from methylene groups in ethyl or from methyl groups located at branch points in alkyl groups or substituents on alicyclic ring structures. The peaks near 30 ppm (28 and 31 ppm) arise from methylene groups flanked by two other methylene groups or CH2groups in cyclic compounds which are common in terpenes. The peaks between 35 and 42 ppm arise from methine carbons or methylene carbons adjacent to at least one quaternary carbon. The peak at 46 ppm is due to quaternary carbons such as those found at bridgehead positions and which have substituents attached to the next nearest neighbor. The peak at 72 ppm is due to a CH group with an alcohol or ether group attached. In the spectral region between 100 and 160 ppm five resonance bands can be observed (118,127,133,143, and 146 ppm). Previous reports of NMR spectra of amber and resinites have identified a resonance band near 108 ppm which is due to the terminal carbon in a vinyl group (= CH2).l6J6 The Wattis seam resinite seems to be unique by the absence of this peak or the relatively low concentration of such a peak. The proton NMR spectrum of the chloroform soluble fraction of Hiawatha resinite does not permit discrimination of vinyl from the alkene groups observed. The aromatic region of the proton NMR spectrum of a chloroform solution of a commerciallyprepared Hiawatha resin exhibits an aromatic band (6.8-7.2 ppm) that is lower in integrated area than that of the alkene proton region (5.0-5.5 ppm). Hence, the sp2-hybridized carbons appear to be a mixture of alkene and aromatic carbons. In amber samples, aromatic carbons are absent from both IR and NMR data. The 13C resonance peaks observed at 118,143, and 146 ppm are consistent with the chemical shifts of alkene structures which have branch points at the carbon adjacent to the double bond, Le., structures related to the isoprenoid skeletal structure. The peaks at 127 and 133 ppm fall within the range of either simple alkene or aromatic carbons. The spectral region beyond 150 ppm is devoid of any detectable peaks, although carbonyl peaks are found in the commercially prepared resins from the same seam (presumably arising from oxidative processes once the coal is mined and the resinite is processed). Hence, the fresh Wattis seam resinite appears to contain a second unique feature, compared to earlier studies, wherein carbonyl groups are either absent from the structure or appear in only very small quantities. The low oxygen content (3.27%) is consistent with this observation and it would appear that oxygen appears only in the form of an alcohol. Hence, the triple ratio described by Lambert and Frye15 would be 83:17:0 for the fresh Wattis resinite. In the commercially prepared resins, approximately 5 % of the total carbon intensity in a 13C CP/MAS spectrum is associated with carbon-oxygen functional groups (both sp2(45) Botto, R.E.;Wilson, R.;Winam, R.E.Energy fiela 1987,1,173.
and sp3-hybridizedcarbons). The pyrolysis MS and GC/MS data for the pure resinite presented here indicate that the material contains a large amount of (po1y)sesquiterpenoidstructures together with smaller amounts of naphthalenes and phenols. The 13C NMR data are consistent with this finding and further demonstrate that some unique features occur in this resinite. Solvent extraction studies have indicated that the resinite is readily dissolved in organic solvents but a polymeric species is taken up as a colloidal dispersion which can mask the NMR spectral features of the truly solubilized material. The nature of this solubilized material is presently under study. The elemental analysis results suggest an empirical formula C14H21No.100.6 which is certainly more consistent with the inferred (po1y)sesquiterpenoidstructure than with the (po1y)diterpenoic acid structures that have been proposed for most ambers (Beck,12 Langenheim'9 and for Australian (Yallourn) brown coal resinite." The Hiawatha resinite appears to be unique not only in its relatively high abundance in the coal seam and the manner in which it has flowed to fil cleats and fissures in the coal but also in the fact that it has a rather uncommon chemical structure and possible botanical affinity.
IV. Conclusions The studies described above have established that the abundant green flourescing resinite component present in the Wattis seam coal is a polymeric substance composed of sesquiterpenoid monomers or repeat units with a median size of 204 Da. The monomeric components appear to represent a range of different degrees of unsaturation between sesquiterpenes and the aromatic alkylnaphthalene cadalene (MW 198). Since similar sesquiterpenoids occur at a low molecular weight distillable fraction in some lower rank Western coals, it appears possible that the secondary form of green fluorescing resinite which fills cleats and fissures in the Wattis coal is the result of secondary polymerization processes during coalification. Although diterpenoid and triterpenoid moieties have been reported to occur together with sesquiterpenoid components in lower rank Western primarily sesquiterpenoid components were observed in the green fluorescing Wattie seam concentrate examined in this study. It is hypothesized that sesquiterpenoid resin components may be important precursors of extractable alkylnaphthalenes in high-voltage bituminous Western coals. Acknowledgment. This work was supported by Department of Energy Conta& No. DEFG22-82PC50812,the Consortium for Fossil Fuel Liquefaction Science, Contract No. UKRF-4-21816-87, the Center for Advanced Coal Technology, and by the Advanced Combustion Engineering Research Center, Grant No. CDR-8522618. Funds for the Center are received from the National Science Foundation, the State of Utah, and 21 industrial participants. Registry No. C16H18,483-78-3.
